Granular media filters are commonly used to remove particulate solids from water in water and wastewater treatment plants. These filters typically employ sand, crushed coal, granular activated carbon (GAC), crushed garnet or a combination of these or similar granular materials as filter media. The water to be filtered is passed through the filter media and the particulate solids are trapped at the surface of the filter media and in the interstitial spaces within the filter media. The entrapped particulate solids are removed from the filter media by a periodic washing operation called backwashing in which water or a water/air combination is passed upwardly through the filter media at sufficient velocities to carry the particulate solids upwardly. The backwash water and entrained particulate solids are intercepted by a backwash water collector typically consisting of a pipe or trough. Because of turbulence caused by the backwashing process, grains of the filter media can become entrained in the backwash water stream and are carried over the overflow weir edge of the backwash trough and are removed or lost from the filter. The media loss is particularly severe when using low density media such as crushed coal or when using air to assist in scouring the entrapped particulate solids from the filter.
One prior art granular media filter is shown in U.S. Pat. No. 4,076,625 and includes means intended to reduce media loss and consisting of baffles placed adjacent to or surrounding the backwash trough to intercept and deflect the air used in the backwash process. The baffles reduce the velocity and turbulence of water currents near the overflow weir edge of the backwash trough to thereby reduce media loss.
Biological reactors are commonly used to remove biological nutrients and/or organic materials from water and wastewater in biological treatment plants. These reactors typically employ biological organisms which remove the organic constituents in the wastewater. The reaction causes an accumulation of granulated or flocculated biomass and the production of gas through the conversion of the organic waste constituents to methane and/or carbon dioxide.
A typical biological reactor includes a bed of biological organisms. Wastewater containing organic constituents passes into the reactor and flows upwardly through the bed of biological material. The biological organisms are able to contact and react with a greater portion of the organic constituents in the wastewater.
As the biological organisms react with the constituents in the wastewater, the biological organisms grow and become less dense. Less dense biomass becomes buoyant and rises toward the wastewater collection trough. The upward flow of liquid and the gas produced in the reaction also tends to cause media and biomass to flow upwardly toward the collection trough.
To retain the media and biomass in the biological reactor, a series of overlapping baffles are typically positioned in the upper portion of the reactor. The baffles divert the media and biomass away from the exit zone and collection trough. The baffles reduce the upward velocity of the wastewater so that biomass entering the exit zone settle downwardly and re-enter the biomass zone and biomass bed.